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Transcript of Potato Lab
Potatoes Immersed in Glucose Solutions
Draining off Excess Glucose
Top View - Potatoes in Glucose
Potato Cores in Different Moles of Glucose
Conclusions - 1
Our hypothesis of “If potatoes are placed in solutions of increasing molarity of glucose then the potato’s mass change will decrease and become negative because osmosis will cause the water molecules to move to the area with less solutes (glucose).” was supported. In our experiment we found the greater molarity of glucose in the solution in which the potato was submerged, the greater the mass decrease. We collected data for 6 cores of potatoes for 7 trials, and the average percentage changes supported our hypothesis. For example, we saw a 0.64% mass change for the potato immersed in a 0.1 M glucose solution, whereas the potato performed a -3.17% mass difference when soaked in a 1.0 M glucose solution (our highest glucose molarity). Since the potato placed in 0.1 M of glucose experienced a positive change in mass, it shows that potatoes have a low solute concentration . From our graph we can conclude potatoes have an osmotic potential of 0.2 M, which isotonic point of no net movement of water molecules across the potato cell's membrane. This parallels with the background research, where we found potatoes have little or no glucose.
A fundamental design flaw in our experiment occurred, as we did not have the preferred glucose solutions in stock. Resulting in us jumping from 0.1 M - 0.6 M, then proceeding upwards by 0.2 to 1.0, We also received several outliers in our data, which was probably due to a mistakes in uncontrolled variables, such as the difference in where we cut the cores (closer to the edge or center of the potato). We also used two potatoes which we could not control their age, or previous conditions affecting their osmotic potential. To achieve more accurate data in the future, we could run more trials, and cut the potatoes with more uniformity and precision. We should have realized what a low glucose concentration potatoes have from our data, and soaked them in solutions with molarity ranging from 0.1 - 0.0, instead of 1.0 - 0.1, to have a better chance of finding a more accurate isotonic solution. Or submerge them in the solutions for longer, to have more time for the concentrations to reach equilibrium. Thus being able to conclude a more precise solute molarity in potatoes.
If potatoes are placed in solutions of increasing molarity of glucose then the potato’s mass change will decrease and become negative because osmosis will cause the water molecules to move to the area with less solutes (glucose).
What is the osmotic potential of potato cells?
Graph & Data Analysis -2
- Each cut potato chunk has no skin, and is made completely out of inner potato
-All potatoes appear to be the same rectangular shape before and after submerged in the glucose solution
- No potato chunk undertake a noticeable color change, and all remain the similar shade of yellow.
-While handling the potatoes to dry them for weighing, we noticed the cores submerged in the higher concentrations were softer and the rigid ones soaked in the lower molarity solutions.
-All potato cores were completely submerged within the glucose solutions for the full 10 minutes.
Osmotic Potential of Potatoes
Adithi Sanjay, Tess Casher, Elodie Compton, & Alveena Majeed.
Block: 6 Honors Biology
Our background research showed carbohydrates, such as starch, make up 21% of the composition of potatoes. Starch contains alpha glucose molecules joined by glycosidic bonds; it is not soluble in water. We questioned the solute molarity in potatoes, and researched it by attempting to find an isotonic solution. We hypothesized the potatoes will decrease in mass more if placed in higher glucose molarity solution, because water molecules will move to an area with more solutes. We peeled, cut the potatoes into cores, keeping a uniform mass of 2.06-2.12 g before placing them in different glucose molarity solutions for 10 minutes, recording their mass before and after for comparison. Our graph showed a negative correlation between the increasing molarity in solutions, and the percentage change of the mass of the potato, supporting our hypothesis. We plotted the average percentage changes and graphed two lines to include and exclude our outlier. From our graph we concluded that potatoes have approximately a concentration of 0.197 M; this concentration is much lower than expected. In future experiments we could soak the potatoes in solutions of lower glucose molarity, or for longer amounts of time to get closer to finding an isotonic solution, and achieve equilibrium.
- Potatoes have lots of starch (approx. 17g carbohydrate per potato serving size 150 g)
- Baked russet potatoes are 21% carbohydrates, it is estimated a medium sized russet potato has 35 g of carbohydrates, and 0.6 grams of glucose.
-Leaving the skin of the potatoes will affect their osmosis patterns, limiting water movement.
- Starch is a carbohydrate means it contains a lot of glucose joined by glycosidic bonds
- Photosynthesis is the long and complex process of turning carbon dioxide into glucose, which is mainly stored in starch granules within the chloroplasts
- Glucose is soluble in water, however glucose in the form of starch is not, so it may be stored much more compactly within the food.
- Glucose molecules are bound into starch using hydrolyzed alpha bonds.
-In lower glucose concentration a potato is placed in, the mass may increase as water will enter the potato. Resulting it becoming hard, and turgid.
- If potatoes are placed in an increasing glucose concentration, more water will leave the potato resulting in decreasing mass, and a potato will become softer (plasmolyse).
Molarity of glucose in solution potatoes are placed in.
The percentage of mass changed in the potato.
Amount of solution, mass of potato chunks, time spent submerged in solution, environmental conditions (light exposure, temperature…), method taking potatoes in and out of solution, approximate shape of potato chunks, size of beakers.
1) Peel potato and use fry cutter to cut into sizes of approximately 2.5 cm long, 1 cm high, and 1 cm wide, and have a mass of 2.06-2.12 g without skin. Make 28 pieces (CAUTION - Mind fingers while skinning potato and using fry cutter).
2) Label 4 separate identical beakers with 0.1M, 0.6M, 0.8M, & 1.0 M of glucose.
3) Fill each beaker with 20 ml of appropriate solution into correctly labeled beaker. (These solutions are not toxic, but not recommended to be digested)*
3) Weigh potato cores, and record initial mass, and which beaker they will be placed in
4) At the same time, and in the same method, place all 4 potato cores into appropriate beaker, and begin 10 minute timer
4) Once the 10 minutes are up, take out all potato chunks as the same time by lifting them with a spoon and lightly dab dry with paper towel in a similar method.
5) Measure and record final mass on a weigh scale
6) Calculate the percentage of mass changed. (Final Mass-Initial Mass / Initial Mass x 100)
7) Repeat steps 3-6 six more times to have a total of 7 trials
*This lab is rather safe, however still use caution in the lab. It is recommend to wear safety glasses, as you may be handling glass beakers.
Looking at our data table, we have the initial and final mass of the potato, and the average percentage change.
How we came across the percentage change:
Example (0.6 M glucose, initial mass: 2.13 g, final mass: 2.07). 2.07 - 2.13 = -0.06 | -0.06/2.13 = -0.0281|
-0.0281 x 100 = -2.81
Then we found the average of all the percentage changes.
Example (0.6 M glucose: -1.88, -2.81, -1.42, -2.87, -5.31, -2.30, -2.40)
-1.88 + -2.81 + -1.42 + -2.87 + -5.31 + -2.30 + -2.40 = -18.99 |
-18.99/7 = -2.71
The average makes it easier for us to compare the data, and it also includes each one of our trials.
Data Analysis -1
Bursso, Jessica. "Glucose of Potatoes." SF Gate. Demand Media, n.d. Web. 4 Jan. 2014. <http://healthyeating.sfgate.com/glucose-potatoes-5024.html>.
"Food Summary, Potato." Self Nutrition and Data. N.p., n.d. Web. 4 Jan. 2014. <http://nutritiondata.self.com/facts/vegetables-and-vegetable-products/2770/2>.
"Potato." Wikipedia. Wikipedia, n.d. Web. 6 Jan. 2014. <http://en.wikipedia.org/wiki/Potato>.
"Potatoes Nutritional Information." Potato. N.p., n.d. Web. 7 Jan. 2014. <http://www.potato.ie/nutritional-information/>.
"Sugar Concentration of a Potato." 123 Help Me. N.p., n.d. Web. 6 Jan. 2014. <http://www.123helpme.com/view.asp?id=120838>.
"Quick Calcs." Graphpad. N.p., 2014. Web. 13 Jan. 2014.
As shown above, we received outliers in our data probably due to accidentally uncontrolled variables. We have graphed the percentage changed averages including and excluding the outliers. At higher glucose concentrations, the average percentage change begins to level off. This is because the pressure is increasing resulting in the potato cells are becoming plasmolysed.
- 1 large potato
- Cutting board
- Fry cutter for perfectly same sized potato cores
- Scale to record mass
- 4 plastic spoons to take pieces out at the same time
- Stopwatch to track time spent immersed within glucose solutions
- 4x50 ml identical beakers
- 20 ml of 4 types of glucose with varying molarity (0.1, 0.6, 0.8, 1.0)
We decided to compare the two groups which we thought to be the most different: 0.1 M and 1.0 M. Our suspicions were confirmed with a t test, which tells us that the amount of glucose in potatoes is much closer to 0.1 M than 1.0 M.